Polycarbonate resin is a polymer in which aromatic or aliphatic dioxy compounds are connected to each other by a carbonate ester and is used in many fields as it is excellent in not only transparency and heat resistance but also mechanical properties such as impact resistance. It is widely used in application fields in which high transparency is required, such as lighting covers and protective covers for transmission type displays, making use of high light transmittance and excellent transparency typified by extremely low haze of a polycarbonate resin.
However, the transparency of a polycarbonate may be not satisfactory when it is used in liquid crystal displays for personal computers and cell phones and lighting equipment. That is, a material having little light attenuation from a light source, that is, light guiding properties is desired for a surface light source body which receives light from a light source and emits light from the surface so as to emit light even from the end face uniformly and efficiently.
Since a material which is light in weight and excellent in workability is also desired, polymethyl methacrylate (to be abbreviated as PMMA hereinafter) out of thermoplastic resins has been used as the most suitable material. However, PMMA is not always satisfactory in terms of heat resistance, impact resistance and flame retardancy, and its use environment is limited in the above applications.
Meanwhile, although the polycarbonate resin can be used without any problem in terms of heat resistance and impact resistance, its transparency is not as high as that of PMMA and therefore, it has not been used for application fields in which light guiding properties are required. In this situation, display devices and lighting equipment which comprise a light emitting diode (LED) as a light source are attracting attention from the viewpoint of long service life and low power consumption. Since LED is an electric appliance which emits light with a polar direct current, flame retardancy required for ordinary electric and electronic equipment is required for optical members comprising an LED as a light source. Actually, new standards such as UL8750 (LED Equipment for Use in Lighting Produce) were established for final products comprising an LED as a light source in December 2009 in the U.S.A.
An example in which the light guiding properties of a polycarbonate have been improved is a composition prepared by mixing an aromatic polycarbonate resin with an acrylic resin having high transparency (Patent Documents 1 to 4) A resin composition for light guides prepared by mixing a polycarbonate having a viscosity average molecular weight of 13,000 to 15,000 with a stabilizer and a release agent was reported (Patent Document 5). Although the light guiding properties of the polycarbonate were improved, these patent documents are silent about flame retardancy. Also, a polycarbonate resin composition which has flame retardancy and transparency was reported (Patent Documents 6 to 9). However, these reports mention transparency but not light guiding properties.
(Patent Document 1) Japanese Patent No. 3100853
(Patent Document 2) Japanese Patent No. 3330498
(Patent Document 3) Japanese Patent No. 3516908
(Patent Document 4) JP-A 2006-201667
(Patent Document 5) JP-A 2007-204737
(Patent Document 6) Japanese Patent No. 2852201
(Patent Document 7) Japanese Patent No. 4060500
(Patent Document 8) Japanese Patent No. 3129374
(Patent Document 9) JP-A 2002-80713